php把读取xml 文档并转换成json数据代码

/*
<?xml version='1.0' encoding='utf-8' ?>
<root cityid="0" classid="0" placeid="0" yy="0" mm="0" pg="1" ps教程="20" maxPage="1" num="1" serverIP="58.57.65.195">
<expo ID="3889" cityid="53" city="北京" classid="0" classname="建筑/装潢/五金" place="中国国际展览中心" placeid="0" tm1="2010-6-3" tm2="2010-6-5" title="20会" Address="北
里河路13号">
<![CDATA[2010北京第十五届中件系列]]>
</expo>
</root>

*/

<?php
$url = "http://www.111cn.net/xml.xml";

$dom = new DOMDocument();
$dom->load($url);
$root = $dom->documentElement;
$arr=array();
foreach ($root->childNodes as $item)
{
        if($item->hasChildNodes())
        {
                $tmp=array();
                foreach($item->childNodes as $one)
                {
                        $tmp[$one->tagName]=$one->nodeValue;
                }
               
                $arr[$item->tagName]=$tmp;
        }
}

$jsonStr = json_encode($arr);

var_dump($jsonStr);

/*

*/
?>